Iron (Fe) is a common element with widespread industrial applications, including construction, transportation, and manufacturing. In the context of optical systems, iron is not typically used in its elemental form due to its propensity for oxidation and poor transparency to light. However, iron-doped materials, such as iron-doped silica, are used for specialized applications such as in optical fibers for telecommunications and sensors. Iron is also used in the form of thin films in some optical components where its magnetic properties are advantageous. Additionally, mirrors for high-power laser applications can be made from polished iron or iron alloys, though this is less common than materials like copper. Overall, while elemental iron is not a primary material in optical applications, its properties are leveraged in various forms and composites for specialized uses.